Increasingly strict legal regulations concerning permitted pollutant emissions of motor vehicles in which internal combustion engines are arranged necessitate keeping the pollutant emissions during operation of the internal combustion engine as low as possible. On the one hand this may be affected by reducing the pollutant emissions which arise during the combustion of the air fuel mixture in the respective cylinder of the internal combustion engine.
On the other hand exhaust gas aftertreatment systems are in use in internal combustion engines which convert the pollutant emissions arising during the combustion process of the air fuel mixture in the respective cylinders to harmless substances.
For example, to this end exhaust gas catalytic converters are employed, which convert carbon monoxide, hydrocarbon and nitrogen oxides to harmless substances.
The selective control of the generation of the pollutant emissions during combustion as well as the conversion of the toxic components by means of a catalytic converter having a high degree of efficiency require a precisely adjusted air fuel ratio in the respective cylinder.
From the reference book “Handbuch Verbrennungsmotoren”, editors Richard van Basshuysen, Fred Schäfer, second edition, Vieweg & Sohn Verlagsgesellschaft mbH, June 2002, pp. 559 to 561, a linear lambda control having a linear lambda oxygen sensor is known, which is arranged upstream of an exhaust gas catalytic converter, and having a binary lambda oxygen sensor, which is arranged downstream of the exhaust gas catalytic converter. A lambda set point is filtered by means of a filter, the gas propagation delay and the sensor behaviour are accounted for. The lambda set point such filtered serves as the control variable of a PII2D oxygen sensor control, whose actuating variable serves as an adjustment for the amount of fuel injected.
Associated with the lambda control one or multiple lambda oxygen sensors become important. On this account increasingly stringent legal regulations are implemented, which require a very strict monitoring of the respective lambda oxygen sensors. For instance, in line with the legislation of the State of California (Title 13, California Code Regulations, Section 1968.2, Chapter (e) (7)), besides an existing dynamic diagnostics of a lambda oxygen sensor for the detection of a dynamic symmetrical deterioration arranged upstream of an exhaust gas catalytic converter additionally the detection of a asymmetrically deteriorated lambda oxygen sensor is required. In this context a dynamic symmetrical deterioration of the lambda oxygen sensor is to be understood such that its response behaviour is delayed symmetrically after a change in the air fuel ratio from lean to rich and vice versa. During a dynamic asymmetric deterioration only the response behaviour of one of both transitions shows a slowing down of the signal reaction. The slowing down of the signal reaction here expresses itself regularly in a delay of the step response as a reaction to a variation of the mixture, in a reduced slope of the shoulder or in a combination of both. In this context it is a particular challenge to achieve diagnostic results which are robust and suitable for operation in the field throughout the required lifetime and considering all possible operating conditions, in particular considering tightened demands concerning mileages of up to 150,000 miles.